Reactive liquid based gas storage and delivery systems

ABSTRACT

This invention relates generally to an improvement in low pressure storage and dispensing systems for the selective storing of gases having Lewis acidity or basicity, and the subsequent dispensing of said gases at pressures, e.g., generally below 5 psig and typically below atmospheric pressure, by modest heating, pressure reduction or both. The improvement resides in storing the gases in a reversibly reacted state within a reactive liquid having opposing Lewis basicity or acidity.

BACKGROUND OF THE INVENTION

Many processes in the semiconductor industry require a reliable sourceof process gases for a wide variety of applications. Often these gasesare stored in cylinders or vessels and then delivered to the processunder controlled conditions from the cylinder. The semiconductormanufacturing industry, for example, uses a number of hazardousspecialty gases such as phosphine (PH₃), arsine (AsH₃), and borontrifluoride (BF₃) for doping, etching, and thin-film deposition. Thesegases pose significant safety and environmental challenges due to theirhigh toxicity and pyrophoricity (spontaneous flammability in air). Inaddition to the toxicity factor, many of these gases are compressed andliquefied for storage in cylinders under high pressure. Storage of toxicgases under high pressure in metal cylinders is often unacceptablebecause of the possibility of developing a leak or catastrophic ruptureof the cylinder.

In order to mitigate some of these safety issues associated with highpressure cylinders, on-site electrochemical generation of such gases hasbeen used. Because of difficulties in the on-site synthesis of thegases, a more recent technique of low pressure storage and deliverysystems has been to adsorb these gases onto a solid support. Thesestorage and delivery systems are not without their problems. They sufferfrom poor capacity and delivery limitations, poor thermal conductivity,and so forth.

The following patents and articles are illustrative of low pressure, lowflow rate gas storage, and delivery systems.

U.S. Pat. No. 4,744,221 discloses the adsorption of AsH₃ onto a zeolite.When desired, at least a portion of the AsH₃ is released from thedelivery system by heating the zeolite to a temperature of not greaterthan about 175° C. Because a substantial amount of AsH₃ in the containeris bound to the zeolite, the effects of an unintended release due torupture or failure are minimized relative to pressurized containers.

U.S. Pat. No. 5,518,528 discloses delivery systems based on physicalsorbents for storing and delivering hydride, halide, and organometallicGroup V gaseous compounds at sub-atmospheric pressures. Gas is desorbedby dispensing it to a process or apparatus operating at lower pressure.

U.S. Pat. No. 5,704,965 discloses sorbents for use in storage systemswhere the sorbents may be treated, reacted, or functionalized withchemical moieties to facilitate or enhance adsorption or desorption offluids. Examples include the storage of hydride gases such as arsine ona carbon sorbent.

U.S. Pat. No. 5,993,766 discloses physical sorbents for sub-atmosphericstorage and dispensing of fluids in which the sorbent can be chemicallymodified to affect its interaction with selected fluids. For example, asorbent material may be functionalized with a Lewis basic amine group toenhance its sorbtive affinity for B₂H₆ (sorbed as BH₃).

U.S. Pat. No. 6,277,342 discloses a method for delivering Brønsted basicgases via reversibly protonating the gases using at least one polymersupport bearing acid groups. The resulting salt formed from theacid/base reaction becomes sorbed to the polymer support.

BRIEF SUMMARY OF THE INVENTION

This invention relates generally to an improvement in low pressurestorage and dispensing systems for the selective storing of gases havingLewis basicity or acidity, and the subsequent dispensing of said gases,generally at pressures of 5 psig and below, typically at subatmosphericpressures, e.g., generally below 760 Torr, by pressure differential,heating, or a combination of both. The improvement resides in storingthe gases in a reversibly reacted state with a reactive liquid havingLewis acidity or basicity.

Several advantages for achieving safe storage, transportation, anddelivery of gases having Lewis basicity or acidity can be achieved.These include:

-   an ability to maintain a reliable source of these gases wherein the    gases are maintained near or below atmospheric pressure during    shipping and storage;-   an ability to store and deliver gases in essentially pure form;-   an ability to manage the problems associated with the transfer of    heat during gas loading and dispensing;-   an ability to allow for mechanical agitation and pumping, thereby    making operations such as compound transfer more efficient;-   an ability to optimize the binding affinity for a given gas through    choice of reactive component; and,-   an ability to obtain high gas (or working) capacities compared to    the surface adsorption and chemisorption approaches associated with    solid adsorbents.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic perspective representation of a storage anddispensing vessel with associated flow circuitry for the storage anddispensing of gases such as phosphine, arsine, and boron trifluoride.

FIG. 2 is a graph of working capacity for phosphine for a number ofreactive liquids.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an improvement in a low-pressure storage anddelivery system for gases having Lewis basicity or acidity, particularlyhazardous specialty gases such as phosphine, arsine and borontrifluoride, which are utilized in the electronics industry. Theimprovement resides in storing the gases in a continuous liquid mediumby effecting a reversible reaction between a gas having Lewis basicitywith a reactive liquid having Lewis acidity or, alternatively, a gashaving Lewis acidity with a reactive liquid having Lewis basicity.

The system for storage and dispensing of a gas comprises a storage anddispensing vessel constructed and arranged to hold a liquid-phase mediumhaving a reactive affinity for the gas to be stored, and for selectivelyflowing such gas into and out of such vessel. A liquid-phase mediumhaving a reactive affinity for the gas is disposed in the storage anddispensing vessel. A dispensing assembly is coupled in gas flowcommunication with the storage and dispensing vessel, and constructedand arranged for selective, on-demand dispensing of the gas having Lewisacidity or Lewis basicity, by thermal and/or pressuredifferential-mediated evolution from the reactive liquid-phase medium.The dispensing assembly can be constructed and arranged:

-   (i) to provide, exteriorly of said storage and dispensing vessel, a    pressure below said interior pressure, to effect evolution of the    gas from the reactive liquid-phase medium, and flow of gas from the    vessel through the dispensing assembly; and/or-   (ii) to provide means for removal of heat of reaction of the gas    with the reactive liquid and for heating the reactive liquid to    effect evolution of the gas therefrom, so that the gas flows from    the vessel into the dispensing assembly.

Thus, in one aspect, the invention relates to a system for the storageand delivery of a gas having Lewis basicity, comprising a storage anddispensing vessel containing a reactive liquid having Lewis acidity andhaving a reactive affinity for the gas having Lewis basicity. In anotheraspect, the invention relates to a system for the storage and deliveryof a gas having Lewis acidity, comprising a storage and dispensingvessel containing a reactive liquid having Lewis basicity and having areactive affinity for the gas having Lewis acidity.

A further feature of the invention is that the gas reactively storedwithin the reactive liquid is readily removable from the reactive liquidby pressure-mediated and/or thermally-mediated methods. Bypressure-mediated evolution is meant evolution involving theestablishment of pressure conditions, which typically range from 10⁻¹ to10⁻⁷ Torr at 25° C., to cause the gas to evolve from the reactiveliquid. For example, such pressure conditions may involve theestablishment of a pressure differential between the reactive liquid inthe vessel, and the exterior environment of the vessel, which causesflow of the fluid from the vessel to the exterior environment (e.g.,through a manifold, piping, conduit or other flow region or passage).The pressure conditions effecting gas evolution may involve theimposition on the reactive liquid of vacuum or suction conditions whicheffect extraction of the gas from the vessel.

By thermally-mediated evolution is meant heating of the reactive liquidto cause the evolution of the gas from the reactive liquid so that thegas can be withdrawn or discharged from the vessel. Typically, thetemperature for thermal-mediated evolution ranges from 30° C. to 150° C.Because the complexing medium is a continuous liquid, as opposed to aporous solid medium as employed in the prior art processes, heattransfer is facilitated.

To facilitate an understanding of the storage and delivery system interms of the general description above, reference is made to FIG. 1. Thestorage and dispensing system 10 comprises storage and dispensing vessel12 such as a conventional gas cylinder container of elongate character.In the interior volume 14 of such vessel is disposed a liquid 16 of asuitable reactivity with the gas to be stored. The vessel 12 is providedat its upper end with a conventional cylinder head gas dispensingassembly 18, which includes valves, regulators, etc., coupled with themain body of the cylinder 12 at the port 19. Port 19 allows gas flowfrom the reactive liquid retained in the cylinder into the dispensingassembly 18. Optionally, the vessel can be equipped with an on/off valveand the regulator provided at the site for delivery.

The storage and delivery vessel 12 may be provided with internal heatingmeans (not shown) which serves to thermally assist in shifting theequilibrium such that the gas bonded to the reactive liquid is released.Often, the gas stored in the reactive liquid is at least partially, andmost preferably fully, dispensed from the storage and dispensing vesselcontaining the gas by pressure-mediated evolution. Such pressuredifferential may be established by flow communication between thestorage and dispensing vessel, on the one hand, and a vacuum or lowpressure ion implantation chamber, on the other. The storage anddelivery vessel 12 may also be provided with a means of agitation (notshown) which serves to enhance the rate of gas diffusion from thereactive liquid.

The storage and delivery vessel 12 may be used as the reactor itself inthat a reactive liquid can be transferred into the vessel and the gassubsequently added under conditions for forming the reaction complex insitu within the vessel. The reactive complex comprised of the reactiveliquid and gas can also be formed external to the storage and deliverysystem and transferred into the storage vessel 12.

The key to the process described herein is the use of a reactive,nonvolatile liquid for storage and delivery of the gas having opposingLewis acidity or Lewis basicity to that of the gas. The selection of thereactive liquid for association with the gas, whether Lewis basic orLewis acidic, is to provide for a working capacity within a pressurerange from 20 to 760 Torr of at least 0.5 mole of gas per liter ofliquid, preferably greater than 1 mole of gas per liter of liquid, (e.g.34 grams of PH₃, 78 grams of AsH₃, 28 grams of B₂H₆, or 68 grams of BF₃per liter of liquid), and allow for removal from the reactive liquid ofat least 15%, preferably at least 50%, and most preferably at least 65%of the reacted gas within a working pressure range of from 20 to 760Torr over a temperature range from subambient, e.g., 0° C., to 150° C.

A suitable reactive liquid has low volatility and preferably has a vaporpressure below about 10⁻² Torr at 25° C. and, more preferably, below10⁻⁴ Torr at 25° C. In this way, the gas to be evolved from the reactiveliquid can be delivered in substantially pure form and withoutsubstantial contamination from the reactive liquid carrier. Liquids witha vapor pressure higher than 10⁻² Torr may be used if contamination canbe tolerated. If not, a scrubbing apparatus may be required to beinstalled between the liquid sorbent and process equipment. In this way,the reactive liquid can be scavenged to prevent it from contaminatingthe gas being delivered. Ionic liquids have low melting points (i.e.typically below room temperature) and typically decompose beforevaporizing, usually at temperatures above 200° C., which make them wellsuited for this application.

Ionic liquids can act as a reactive liquid, either as a Lewis acid orLewis base, for effecting reversible reaction with the gas to be stored.These reactive ionic liquids have a cation component and an anioncomponent. The acidity or basicity of the reactive ionic liquids then isgoverned by the strength of the cation, the anion, or by the combinationof the cation and anion. The most common ionic liquids comprise salts ofalkylphosphonium, alkylammonium, N-alkylpyridinium orN,N′-dialkylimidazolium cations. Common cations contain C₁₋₁₈ alkylgroups, and include the ethyl, butyl and hexyl derivatives ofN-alkyl-N′-methylimidazolium and N-alkylpyridinium. Other cationsinclude pyridazinium, pyrimidinium, pyrazinium, pyrazolium, triazolium,thiazolium, and oxazolium.

Also known are “task-specific” ionic liquids bearing reactive functionalgroups on the cation. Such ionic liquids can be prepared usingfunctionalized cations containing a Lewis base or Lewis acid functionalgroup, and these ionic liquids can be used here. Task specific ionicliquids often are aminoalkyl, such as aminopropyl; ureidopropyl, andthioureido derivatives of the above cations. Specific examples oftask-specific ionic liquids containing functionalized cations includesalts of 1-alkyl-3-(3-aminopropyl)imidazolium,1-alkyl-3-(3-ureidopropyl)imidazolium,1-alkyl-3-(3-thioureidopropyl)imidazolium,1-alkyl-4-(2-diphenylphosphanylethyl)pyridinium,1-alkyl-3-(3-sulfopropyl)imidazolium, andtrialkyl-(3-sulfopropyl)phosphonium.

A wide variety of anions can be matched with the cation component ofsuch ionic liquids for achieving Lewis acidity. One type of anion isderived from a metal halide. The halide most often used is chloridealthough the other halides may also be used. Preferred metals forsupplying the anion component, e.g. the metal halide, include copper,aluminum, iron, zinc, tin, antimony, titanium, niobium, tantalum,gallium, and indium. Examples of metal chloride anions are CuCl₂ ⁻,Cu₂Cl₃ ⁻, AlCl₄ ⁻, Al₂Cl₇ ⁻, ZnCl₃ ⁻, ZnCl₄ ²⁻, Zn₂Cl₅ ⁻, FeCl₃ ⁻, FeCl₄⁻, Fe₂Cl₇ ⁻, TiCl₅ ⁻, TiCl₆ ²⁻, SnCl₅ ⁻, SnCl₆ ²⁻,etc.

As is known in the synthesis of ionic liquids, the type of metal halideand the amount of the metal halide employed has an effect on the acidityof the ionic liquid. For example, when aluminum trichloride is added toa chloride precursor, the resulting anion may be in the form AlCl₄ ⁻orAl₂Cl₇ ⁻. The two anions derived from aluminum trichloride havedifferent acidity characteristics, and these differing aciditycharacteristics impact on the type of gases that can be reactivelystored.

Room temperature ionic liquids can be formed by reacting a halidecompound of the cation with an anion supplying reactant.

Examples of halide compounds from which Lewis acidic or Lewis basicionic liquids can be prepared include:

-   1-Ethyl-3-methylimidazolium bromide;-   1-Ethyl-3-methylimidazolium chloride;-   1-Butyl-3-methylimidazolium bromide;-   1-Butyl-3-methylimidazolium chloride;-   1-Hexyl-3-methylimidazolium bromide;-   1-Hexyl-3-methylimidazolium chloride;-   1-Methyl-3-octylimidazolium bromide;-   1-Methyl-3-octylimidazolium chloride;-   Monomethylamine hydrochloride;-   Trimethylamine hydrochloride;-   Tetraethylammonium chloride;-   Tetramethyl guanidine hydrochloride;-   N-Methylpyridinium chloride;-   N-Butyl-4-methylpyridinium bromide;-   N-Butyl-4-methylpyridinium chloride;-   Tetrabutylphosphonium chloride; and-   Tetrabutylphosphonium bromide.

When the system is used for storing phosphine or arsine, a preferredreactive liquid is an ionic liquid and the anion component of thereactive liquid is a cuprate or aluminate and the cation component isderived from a dialkylimidazolium salt.

Gases having Lewis basicity to be stored and delivered from Lewis acidicreactive liquids, e.g., ionic liquids, may comprise one or more ofphosphine, arsine, stibine, ammonia, hydrogen sulfide, hydrogenselenide, hydrogen telluride, isotopically-enriched analogs, basicorganic or organometallic compounds, etc.

With reference to Lewis basic ionic liquids, which are useful forchemically complexing Lewis acidic gases, the anion or the cationcomponent or both of such ionic liquids can be Lewis basic. In somecases, both the anion and cation are Lewis basic. Examples of Lewisbasic anions include carboxylates, fluorinated carboxylates, sulfonates,fluorinated sulfonates, imides, borates, chloride, etc. Common anionforms include BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, CH₃COO⁻, CF₃COO⁻, CF₃SO₃ ⁻,p-CH₃–CH₆H₄SO₃ ⁻, (CF₃SO₂)₂N⁻, (NC)₂N⁻, (CF₃SO₂)₃C⁻, chloride, andF(HF)_(n) ⁻. Other anions include organometallic compounds such asalkylaluminates, alkyl- or arylborates, as well as transition metalspecies. Preferred anions include BF₄ ⁻, p-CH₃—C₆H₄SO₃ ⁻, CF₃SO₃ ⁻,(CF₃SO₂)₂N⁻, (NC)₂N⁻(CF₃SO₂)₃C⁻, CH₃COO⁻ and CF₃COO⁻.

Ionic liquids comprising cations that contain Lewis basic groups mayalso be used in reference to storing gases having Lewis acidity.Examples of Lewis basic cations include N,N′-dialkyimidazolium and otherrings with multiple heteroatoms. A Lewis basic group may also be part ofa substituent on either the anion or cation. Potentially useful Lewisbasic substituent groups include amine, phosphine, ether, carbonyl,nitrile, thioether, alcohol, thiol, etc.

Gases having Lewis acidity to be stored in and delivered from Lewisbasic reactive liquids, e.g., ionic liquids, may comprise one or more ofdiborane, boron trifluoride, boron trichloride, SiF₄, germane, hydrogencyanide, HF, HCl, Hl, HBr, GeF₄, isotopically-enriched analogs, acidicorganic or organometallic compounds, etc.

Nonvolatile covalent liquids containing Lewis acidic or Lewis basicfunctional groups are also useful as reactive liquids for chemicallycomplexing gases. Such liquids may be discrete organic or organometalliccompounds, oligomers, low molecular weight polymers, branched amorphouspolymers, natural and synthetic oils, etc.

Examples of liquids bearing Lewis acid functional groups includesubstituted boranes, borates, aluminums, or alumoxanes; protic acidssuch as carboxylic and sulfonic acids, and complexes of metals such astitanium, nickel, copper, etc.

Examples of liquids bearing Lewis basic functional groups includeethers, amines, phosphines, ketones, aldehydes, nitrites, thioethers,alcohols, thiols, amides, esters, ureas, carbamates, etc. Specificexamples of reactive covalent liquids include tributylborane, tributylborate, triethylaluminum, methanesulfonic acid, trifluoromethanesulfonicacid, titanium tetrachloride, tetraethyleneglycol dimethylether,trialkylphosphine, trialkylphosphine oxide, polytetramethyleneglycol,polyester, polycaprolactone, poly(olefin-alt-carbon monoxide),oligomers, polymers or copolymers of acrylates, methacrylates, oracrylonitrile, etc. Often, though, these liquids suffer from excessivevolatility at elevated temperatures and are not suited forthermal-mediated evolution. However, they may be suited forpressure-mediated evolution.

To provide an understanding of the concepts disclosed herein thefollowing are relevant definitions to the process:

DEFINITIONS

Total Capacity (or Capacity): Moles of gas that will react with oneliter of reactive liquid at a given temperature and pressure.

Working Capacity (C_(w)): Moles of gas per liter of reactive liquidwhich is initially stored and is subsequently removable from the liquidduring the dispensing operation, specified for a given temperature andpressure range, typically at 20 to 50° C. over the pressure range 20 to760 Torr.

C_(w)=(moles of reacted gas—moles of gas remaining afterdelivery)/(liters of reactive liquid)

Percent Reversibility: Percentage of gas initially reacted with theliquid which is subsequently removable by pressure differential,specified for a given temperature and pressure range, typically at 20 to50° C. over the pressure range 20 to 760 Torr.

% Reversibility=[(moles of reacted gas—moles of gas remaining afterdelivery)/(moles of initially reacted gas)]*100.

It has been found that good Lewis acid/basic and Lewis basic/acidicsystems can be established from the Gibbs free energy of reaction(ΔG_(rxn)) for a given system. In a storage and delivery system basedupon a reactive liquid and a gas having Lewis acidity or basicity, aΔG_(rxn) range exists for operable temperature and pressure and is from−1 to about −6 kcal/mole. There also exists an optimum ΔG_(rxn) for agiven temperature and pressure range, which corresponds to a maximumworking capacity for the liquid. In reference to the gas PH₃, if themagnitude of ΔG_(rxn), (and thus, K_(eq)) is too small, the reactiveliquid will have insufficient capacity for PH₃. This insufficientcapacity may be compensated for by selecting a reactive liquid with ahigher total capacity (i.e. higher concentration of PH₃ reactivegroups). If the magnitude of ΔG_(rxn) (and thus, K_(eq)) is too large,an insufficient amount of PH₃ will be removable at the desired deliverytemperature. For the reaction of PH₃ with a Lewis acid, A, at 25° C. andin the pressure range 20 to 760 Torr, the optimum value range forΔG_(rxn) is about from −2.5 to −3.5 kcal/mol. For all systems insolution involving the reaction of a single equivalent of gas with asingle equivalent of Lewis acid/base group, the optimum ΔG_(rxn) will beabout −3 kcal/mol at 25° C. and between 20 to 760 Torr. The situation ismore complex for other systems, e.g., if the gas and liquid react togive a solid complex, or if more than one equivalent of a gas reactswith a single equivalent of a Lewis acid/base group.

One of the difficulties in the development of a suitable storage anddelivery system is the matching of a suitable reactive liquid with asuitable gas through prediction of the ΔG_(rxn). To minimizeexperimentation and project the viability of possible systems, quantummechanical methods can be used to elucidate molecular structures.Density Functional Theory (DFT) is a popular ab initio method that canbe used to determine a theoretical value for the change in electronicenergy for a given reaction (ΔE_(rxn)=sum of E_(products)−sum ofE_(reactants)). The following is a discussion for this determination.The calculations are assumed to have an error of approximately ±3kcal/mol.

The reaction of one equivalent of PH₃ gas with one equivalent of a Lewisacid acceptor (A) in the liquid phase to give a reaction product in theliquid phase is represented by the equations:

$\begin{matrix}\begin{matrix}{{{PH}_{3}({gas})}\overset{K_{1}}{\rightleftharpoons}{{PH}_{3}({soln})}} \\\frac{{A + {{PH}_{3}({soln})}}\overset{K_{2}}{\rightleftharpoons}{A—{PH}}_{3}}{{A + {{PH}_{3}({soln})}}\overset{K_{eq}}{\rightleftharpoons}{A—{PH}}_{3}} \\{K_{eq} = {{K_{1}K_{2}} = \frac{\left\lbrack {A{—PH}}_{3} \right\rbrack}{\lbrack A\rbrack\left\lbrack {{PH}_{3}({gas})} \right\rbrack}}}\end{matrix} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

The equilibrium constant for this reaction, K_(eq), is described byequation 1. K_(eq) is dependent upon the change in Gibbs free energy forthe reaction, ΔG_(rxn), which is a measure of the binding affinitybetween PH₃ and A. The relationships between ΔG, K, and temperature (inKelvin) are given in equations 2 and 3.ΔG=ΔH−TΔS  (Equation 2)ΔG=−RTlnK  (Equation 3)

The value ΔE_(rxn) can be used as an approximate value for the change inenthalpy (ΔH, see equation 2). Also, if it is assumed that the reactionentropy (ΔS) is about the same for similar reactions, e.g., reversiblereactions under the same temperature and pressure conditions, the valuescalculated for ΔE_(rxn) can be used to compare against ΔG_(rxn) forthose reactions on a relative basis, i.e., ΔG_(rxn) is approximatelyproportional to ΔE_(rxn). Thus, the values calculated for ΔE_(rxn) canbe used to help predict reactive liquids, including ionic liquids havingthe appropriate reactivity for a given gas.

The following examples are intended to illustrate various embodiments ofthe invention and are not intended to restrict the scope thereof.

EXAMPLES

General Procedure

The following is a general procedure for establishing the effectivenessof reactive liquids for storing and delivering gases in the examples.PH₃ and BF₃ have been used as the descriptive gases for chemicalcomplexation.

In a glove box, a 25 mL or 50 mL stainless steel reactor was chargedwith a known quantity of a liquid. The reactor was sealed, brought outof the glove box, and connected to an apparatus comprising a pressurizedcylinder of pure PH₃ or BF₃, a stainless steel ballast, and a vacuumpump vented to a vessel containing a PH₃ or BF₃ scavenging material. Thegas regulator was closed and the experimental apparatus was evacuated upto the regulator. Helium pycnometry was used to measure ballast, pipingand reactor headspace volumes for subsequent calculations. The apparatuswas again evacuated and closed off to vacuum. The following steps wereused to introduce PH₃ or BF₃ to the reactor in increments: 1) thereactor was isolated by closing a valve leading to the ballast, 2) PH₃or BF₃ was added to the ballast (ca. 800 Torr) via a mass flowcontroller, 3) the reactor valve was opened and the gas pressure wasallowed to equilibrate while the reactor contents were stirred. Thesesteps were repeated until the desired equilibrium vapor pressure wasobtained. The quantity of PH₃ or BF₃ added in each increment wasmeasured by pressure and volume difference according to the ideal gaslaw. The amount of reacted PH₃ or BF₃ was determined by subtractingtubing and reactor headspace volumes.

Example 1 BMlM⁺Al₂Cl₇ ⁻, Lewis Acidic Ionic Liquid for PH₃

Molecular modeling was used to calculate a binding energy, ΔE_(rxn), forthis Lewis acidic ionic liquid with PH₃. The ionic liquid was modeled asan ion-pair, using 1,3-dimethylimidazolium as the cation, Al₂Cl₇ ₇ ⁻ asthe anion, and it was assumed that one equivalent of PH₃ reacted perequivalent of Al₂Cl₇ ⁻ anion (concentration of Al₂Cl₇ ⁻=3.2 mol/L).Structures were determined based on minimum energy geometry optimizationusing Density Functional Theory (DFT) at the BP level with a doublenumerical (DN**) basis set. This Lewis acidic ionic liquid wascalculated to have a ΔE_(rxn) of 0.71 kcal/mol, which suggests that thereaction is slightly unfavorable, although within the generallimitations of error. To clarify the results of modeling, the followingreaction was run.

In a glove box, 9.07 g of AlCl₃ (2 equivalents) was slowly added to 5.94g (1 equivalent) of 1-butyl-3-methylimidazolium chloride (BMlM⁺Cl). (Itis assumed the anion Al₂Cl₇ ⁻ is formed from the reaction stoichiometry2 equivalents AlCl₃ to 1 equivalent BMlM⁺Cl⁻) A 25 mL reactor wascharged with 4.61 g of BMlM⁺Al₂Cl₇ ⁻ (density=1.2 g/mL) and the generalprocedure for measuring PH₃ reaction was followed. The ionic liquidreacted with 6.9 mmol of PH₃ at room temperature and 776 Torr,corresponding to 1.8 mol PH₃/L of ionic liquid.

The results show % reversibility=89%, working capacity=1.6 mol/L (roomtemperature, 20–760 Torr). The experimental ΔG_(rxn) is approximately−1.9 kcal/mol at 25° C.

These results show that the ionic liquid BMlM⁺Al₂Cl₇ ⁻ is effective as areactive liquid for PH₃ and suitable for use in a storage and deliverysystem as shown in the figure and that the ΔE_(rxn) provides excellentguidance in the selection of a reactive system.

Delivery of the complex formed to storage and delivery system an beeffected by pumping the complex to the vessel.

Example 2 BMlM⁺CuCl₂ ⁻, Lewis Acidic Ionic Liquid For PH₃

In a glove box, 3.10 g of CuCl was slowly added to a flask charged with5.46 g of BMlM⁺Cl⁻ (1:1 stoichiometry). (It is assumed the anion CuCl₂ ⁻is formed from the reaction stoichiometry 1 equivalent CuCl to 1equivalent BMlM⁺Cl⁻). The mixture was stirred overnight and stored. Aglass insert was charged with 7.71 g of the ionic liquid (density=1.4g/mL) and placed into a 50 mL reactor, and the general procedure formeasuring PH₃ reaction was followed. The Lewis acidic ionic liquidreacted with 7.6 mmol of PH₃ at room temperature and 674 Torr,corresponding to 1.4 mol PH₃/L of ionic liquid. Equilibrium data pointswere not obtained and % reversibility and working capacity were notdetermined. But, this reactive liquid is expected to have a high %reversibility and, thus, a sufficient working capacity for a storage anddelivery system.

Example 3 BMlM⁺Cu₂Cl₃ ⁻, Lewis Acidic Ionic Liquid For PH₃

Molecular modeling was used to approximate the effectiveness ofBMlM⁺Cu₂Cl₃ ⁻ as a reactive liquid. The ionic liquid was modeled as anion-pair, using 1,3-dimethylimidazolium as the cation, Cu₂Cl₃ ⁻ as theanion, and it was assumed that one equivalent of PH₃ reacted with eachequivalent of copper (concentration of Cu reactive groups=9.7 mol/L).Structures were determined based on minimum energy geometry optimizationusing Density Functional Theory (DFT) at the BP level with a doublenumerical (DN**) basis set. This Lewis acidic ionic liquid wascalculated to have an average ΔE_(rxn) of −5.5 kcal/mol for its reactionwith PH₃. The results indicate that this ionic liquid should bind PH₃more strongly than BMlM⁺Al₂Cl₇ ⁻ of Example 1. Since ΔG_(rxn) is smallerin magnitude than ΔE_(rxn) and the optimum ΔG_(rxn) for the pressurerange 20 to 760 Torr at room temperature is ca. −3 kcal/mol, the resultsuggests that the binding properties of BMlM⁺Cu₂Cl₃ ⁻ may be well suitedfor reversibly reacting with PH₃ (i.e., high working capacity and high %reversibility).

In a glove box, 11.6 g of CuCl was slowly added to a round bottom flaskcharged with 10.2 g of BMlM⁺Cl⁻ (2:1 stoichiometry). (It is assumed theanion Cu₂Cl₃ ⁻ formed from the reaction stoichiometry 2 equivalents CuClto 1 equivalent BMlM⁺Cl⁻). The mixture was stirred overnight. A glassinsert was charged with 12.02 g of the ionic liquid (density=1.8 g/mL)and placed into a 50 mL reactor, and the general procedure for measuringPH₃ reaction was followed. The ionic liquid reacted with 51 mmol of PH₃at room temperature and 736 Torr, corresponding to 7.6 mol PH₃/L ofionic liquid.

The results show % reversibility=84%, working capacity=6.4 mol/L (roomtemperature, 20–736 Torr). The experimental ΔG_(rxn) is approximately−2.6 kcal/mol at 22° C.

This reactive liquid outperformed the aluminate-based ionic liquid inExample 1 because it has a higher reactive group concentration(theoretical capacity of 9.7 vs. 3.2 mol/L), and its binding affinityfor PH₃ as calculated by ΔE_(rxn) and measured by ΔG_(rxn) is bettermatched compared toBMlM⁺Al₂Cl₇ ⁻.

Example 4 BMlM⁺BF₄ ⁻, Lewis Base Ionic Liquid for PH₃

A 50 mL reactor was charged with 3.99 g of BMlM⁺BF₄ ⁻ and the generalprocedure for measuring PH₃ reaction was followed. The ionic liquid isslightly Lewis basic and it does not react with Lewis basic PH₃,demonstrating that a Lewis acidic species as described in Examples 1 to3 is required for reaction with PH₃. The ΔG_(rxn) reaction is ≧0.

Example 5 BMlM⁺AlCl₄ ⁻, Acid/Base Neutral Ionic Liquid for PH₃

A 50 mL reactor was charged with 9.81 g of BMlM⁺AlCl₄ ⁻ formed by addingAlCl₃ to BMlM⁺Cl (1:1 stoichiometry) and the general procedure formeasuring PH₃ reaction was followed. (It is assumed the anion AlCl₄ ⁻ isformed from the reaction stoichiometry 1 equivalent AlCl₃ to 1equivalent BMlM⁺Cl⁻). The ionic liquid reacted with 0.44 mmol of PH₃,corresponding to about 0.06 mol PH₃/L of ionic liquid. The AlCl₄ ⁻ anionis not Lewis acidic. It is believed that the small amount of PH₃reaction that was observed was likely due to the presence of a smallconcentration of Lewis acidic Al₂Cl₇ ⁻. This example furtherdemonstrates that a Lewis acidic species is required for reaction withPH₃. The ΔG_(rxn) reaction is ≧0.

Example 6 Methanesulfonic Acid, Liquid Brønsted Acid for PH₃

A 50 mL reactor was charged with 8.81 g of methanesulfonic acid(density=1.35 g/mL) and the general procedure for measuring PH₃ reactionwas followed. The acid reacted with 5.6 mmol of PH₃, corresponding to0.86 mol PH₃/L of liquid.

The results show % reversibility=75%, working capacity=0.66 mol/L (roomtemperature, 20–514 Torr). The binding affinity between PH₃ andmethanesulfonic acid is weak, so the total and working capacities aremodest as compared to the reaction systems of Example 1–3 and the %reversibility is high. The system still meets the necessary criteria fora storage and delivery system. The delivered gas, because of the vaporpressure of methanesulfonic acid (˜1 Torr at 25° C.), is contaminatedwith the acid and would require scrubbing prior to use.

Example 7 Triflic Acid, Liquid Brønsted Acid for PH₃

A 50 mL reactor was charged with 4.68 g of triflic acid (density=1.70g/mL) and the general procedure for measuring PH₃ reaction was followed.The acid reacted with 14.7 mmol of PH₃, corresponding to 5.3 mol PH₃/Lof liquid.

The results show % reversibility=0%, working capacity=0 mol/L (roomtemperature, 20–721 Torr). The binding affinity between PH₃ and triflicacid is too strong, so the reaction is irreversible at room temperaturein the pressure range required. This liquid is too volatile forthermal-mediated evolution. It may be suited for a Lewis base gas havingless affinity for the reactive liquid. The delivered gas, because of thehigh vapor pressure of triflic acid (8 Torr at 25° C.), would becontaminated with the acid and would require scrubbing prior to use.

Example 8 TiCl₄, Volatile Liquid Reactive Compound For PH₃

A 50 mL reactor was charged with 12.56 g of TiCl₄ (liquid, density=1.73g/mol), the reactor was cooled to ca. 7° C. in and ice bath, and thegeneral procedure for measuring PH₃ reaction was followed. The ionicliquid reacted with 100.3 mmol of PH₃, corresponding to 13.8 mol PH₃/Lof TiCl₄ at an equilibrium vapor pressure of 428 Torr and a temperatureof 12° C.

The results show % reversibility=41%, working capacity=5.6 mol/L (12°C., 44–428 Torr). The delivered gas, because of the high vapor pressureof the TiCl₄, is contaminated with the volatile titanium complexes andwould require scrubbing prior to use.

Comparative Example 9 Comparison of PH₃ Isotherms for Zeolite 5 Å andReactions of Lewis Acids with PH₃

A series of reaction isotherms for examples 1, 3, 6, 7, and 8 wereacquired for comparison to a reported isotherm for PH₃ adsorption ontozeolite 5 Å. The isotherms are shown in FIG. 2.

In FIG. 2, it is observed that a significant portion of the total PH₃adsorbed on zeolite 5 Å cannot be used under normal dispensingconditions because PH₃ is too strongly adsorbed. The adsorption isothermfor zeolite 5 Å indicates a working capacity of 1.9 mol/L with 66%reversibility between 20 and 710 Torr. Approximately ⅓ of the total PH₃remains adsorbed at a pressure below 20 Torr.

Regarding BMlM⁺Al₂Cl₇ ⁻, it has a lower total capacity and workingcapacity (1.6 mol/L between 20 and 760 Torr) than zeolite 5 Å, but 89%of the PH₃ is reversibly bound down to 20 Torr.

The reaction isotherms obtained for BMlM⁺Cu₂Cl₃ ⁻ show that this ionicliquid has a significantly higher total capacity as well as workingcapacity (6.4 mol/L between 20 and 736 Torr) than zeolite 5 Å. Theamount of PH₃ that is reversibly bound is also significantly higher(about 84% for BMlM⁺Cu₂Cl₃ ⁻ vs. 66% for zeolite 5 Å in the samepressure range).

FIG. 2 shows methanesulfonic acid has a low capacity (0.9 mol/L at 515Torr) because it does not react strongly with PH₃; however, almost allof the PH₃ is reversibly reacted.

Triflic acid has a relatively high capacity (5.3 mol/L at 721 Torr), butessentially none of the reacted PH₃ is removable because the reaction(binding affinity) is too strong.

TiCl₄ reacts with more than a single equivalent of PH₃ and gives amulti-step isotherm. Although TiCl₄ provides a high working capacity(more than 5 mol/L between 44 and 428 Torr), the gas contains impuritiesas a result of the volatility of the titanium species.

Example 10 BMlM⁺BF₄ ⁻, Lewis Basic Ionic Liquid for BF₃

Molecular modeling was used to approximate the effectiveness of BMlM⁺BF₄⁻ as a reactive liquid for the chemical complexation of BF₃. The ionicliquid was modeled as an ion-pair, using 1,3-dimethylimidazolium as thecation, and it was assumed that one equivalent of BF₃ reacted with theanion from each equivalent of BMlM⁺BF₄ ⁻ (concentration of BF₄ ⁻reactive groups=5.4 mol/L). Structures were determined based on minimumenergy geometry optimization using Density Functional Theory (DFT) atthe BP level with a double numerical (DN**) basis set. This Lewis basicionic liquid was calculated to have a ΔE_(rxn) of −5.5 kcal/mol for itsreaction with BF₃.

The modeling results indicate that the binding affinity of this ionicliquid for BF₃ should be similar to the binding affinity betweenBMlM⁺Cu₂Cl₃ ⁻ and PH₃ in Example 3 where ΔE_(rxn) also is calculated tobe −5.5 kcal/mol. Since the reversible reaction between the Lewis acidicBMlM⁺Cu₂Cl₃ ⁻ and Lewis basic PH₃ provides a near optimum workingcapacity, the result suggests that the binding properties of the Lewisbasic BMlM⁺BF₄ ⁻ may be well suited for reversibly reacting with Lewisacidic BF₃ (i.e. high working capacity and high % reversibility).

In a glove box, a 25 mL stainless steel reactor was charged with 8.82 gof BMlM⁺BF₄ ⁻ purchased from Fluka (density=1.2 g/mL), and the generalprocedure for measuring BF₃ reaction was followed. The ionic liquidreacted with 38.4 mmol of BF₃ at room temperature and 724 Torr,corresponding to 5.2 mol BF₃/L of ionic liquid.

The results show % reversibility=70%, working capacity=3.6 mol/L (roomtemperature, 20–724 Torr). The experimental ΔG_(rxn) is −3.4 kcal/mol at22° C. As predicted by molecular modeling, the reaction between BMlM⁺BF₄⁻ and BF₃ behaved similarly to the reaction between BMlM⁺Cu₂Cl₃ ⁻ andPH₃.

Example 11 Tetraglyme, Lewis Basic Liquid for BF₃

Molecular modeling was used to approximate the effectiveness oftetraethyleneglycol dimethylether (tetraglyme) as a reactive liquid.Calculations were carried out using dimethylether and diethylether tomodel the liquid, and it was assumed that one equivalent of BF₃ reactedwith the ether oxygen in both cases. Structures were determined based onminimum energy geometry optimization using Density Functional Theory(DFT) at the BP level with a double numerical (DN**) basis set.Dimethylether was calculated to have a ΔE_(rxn) of −9.1 kcal/mol for itsreaction with BF₃ and diethylether was calculated to have a ΔE_(rxn) of−6.8 kcal/mol for its reaction with BF₃.

The modeling results indicate that the binding affinity of tetraglymefor BF₃ may be too strong to be useful at ambient temperature. Toconfirm the results of modeling, the following reaction was run.

In a glove box, a 25 mL stainless steel reactor was charged with 8.42 gof tetraethyleneglycol dimethyl ether (tetraglyme) purchased from Acros(density=1.0 g/mL), and the general procedure for measuring BF₃ reactionwas followed. The reaction was highly exothermic and reaction was rapid.The liquid reacted with 103.4 mmol of BF₃ at room temperature and 765Torr, corresponding to 12.3 mol BF₃/L of liquid.

As predicted by molecular modeling, tetraglyme reacts strongly with BF₃at room temperature. Essentially none of the chemically complexed BF₃could be removed under vacuum at room temperature. Elevated temperaturesmay by useful for evolving the complexed BF₃, but if the delivered gasis contaminated with tetraglyme, the gas may require scrubbing. Forapplications requiring ambient temperature, the reactive liquid may bebetter suited for Lewis acids that are weaker than BF₃.

In summary, the results show that reactive liquids having Lewis acidityor basicity can be used for storing gases having opposing Lewis basicityor acidity and delivering such gases in substantially pure form atoperating pressures from 20 to 760 Torr over a temperature range from 0to 150° C.

The present invention has been set forth with regard to severalpreferred embodiments, but the full scope of the present inventionshould be ascertained from the claims which follow.

1. In a process for effecting storage of a gas, within a storage anddelivery system comprised of, i) a vessel containing a medium capable ofstoring a gas, and ii) a regulator for delivery of said gas stored insaid medium from said vessel, the improvement selected from the groupconsisting of: storing a gas having Lewis basicity in a reversiblyreacted state within a medium comprised of a reactive liquid havingLewis acidity; and, storing a gas having Lewis acidity in a reversiblyreacted state within a medium comprised of a reactive liquid havingLewis basicity.
 2. The process of claim 1 wherein the reactive liquidfor association with the gas, having Lewis basicity or Lewis acidity, issufficient to provide for a working capacity within a pressure rangefrom 20 to 760 Torr of at least 0.5 mole of gas per liter of liquid andprovide for evolution from the reactive liquid of at least 15% of thecomplexed gas at the operative temperature ranging from 0 to 150CC. 3.The process of claim 2 wherein at least 50% of the stored gas isremovable within a working pressure range of from 20 to 760 Torr at atemperature from 20 to 50° C.
 4. The process of claim 3 wherein the gasis Lewis basic and the reactive liquid is an ionic liquid having Lewisacidity.
 5. The process of claim 4 wherein the Lewis basic gas isselected from the group consisting of phosphine, arsine, stibine,ammonia, hydrogen sulfide, hydrogen selenide, hydrogen telluride, andisotopically-enriched analogs.
 6. The process of claim 5 wherein theionic liquid having Lewis acidity is comprised of a salt ofalkylphosphonium, alkylammonium, N-alkylpyridinium or N,N′-dialkylimidazolium cation.
 7. The process of claim 6 wherein theanion component of such ionic liquids having Lewis acidity is derivedfrom a metal halide selected from the group consisting of copper,aluminum, iron, zinc, tin, antimony, titanium, niobium, tantalum,gallium, and indium halide.
 8. The process of claim 7 wherein the anioncomponent is a metal chloride salt and the metal for supplying the anioncomponent is selected from the group consisting of CuCl₂ ⁻, Cu₂Cl₃ ⁻,AlCl₄ ⁻, Al₂Cl₇ ⁻, ZnCl₃ ⁻, ZnCl₄ ²⁻, Zn₂Cl₅ ⁻, FeCl₃ ⁻, FeCl₄ ⁻, Fe₂Cl₇⁻, TiCl₅ ⁻, TiCl₆ ²⁻, SnCl₅ ⁻, and SnCl₆ ²⁻.
 9. The process of claim 8wherein the vapor pressure of said reactive liquid, having Lewis acidityis less than 10⁻⁴ Torr at 25° C.
 10. The process of claim 9 wherein thegas having Lewis basicity is selected from the group consisting ofphosphine and arsine.
 11. The process of claim 5 wherein the ionicliquid is a cuprate or aluminate salt of alkyiphosphonium,alkylammonium, N-alkylpyridinium and N,N′-dialkylimidazolium cations.12. In a process for effecting storage of a gas, in a storage anddelivery system comprised of, i) a vessel containing a medium capable ofstoring a gas, and ii) a regulator for delivery of said gas stored insaid medium from said vessel, the improvement which comprises: storing agas having Lewis basicity in a reversibly reacted state within a mediumcomprised of a reactive liquid having Lewis acidity; where said gas isselected from the group consisting of arsine and phosphine and saidliquid is an ionic liquid having a dialkyl-imidazolium cation and achlorocuprate or chloroaluminate anion.
 13. The process of claim 12wherein the dialkylimidazolium cation is 1-butyl-3-methylimidazolium andsaid anion is selected from the group consisting of Al₂Cl₇ ⁻, CuCl₂ ⁻and Cu₂Cl₃ ⁻.
 14. In a process for effecting storage of a gas, in astorage and delivery system comprised of, i) a vessel containing amedium capable of storing a gas, and ii) a regulator for delivery ofsaid gas stored in said medium from said vessel, the improvement whichcomprises: storing a gas having Lewis acidity selected from the groupconsisting of diborane, boron trifluoride, boron trichloride, SiF₄,germane, hydrogen cyanide, HF, HCl, Hl, HBr, GeF₄, isotopically-enrichedanalogs, acidic organic, organometallic compounds and mixtures thereof,in a reversibly reacted state within a medium comprised of a reactiveionic liquid having Lewis basicity employing an anion selected from thegroup consisting of BF₄ ⁻, p-CH₃—C₆H₄SO₃ ⁻, CF₃SO₃ ⁻, (CF₃SO₂)₂N⁻,(NC)₂N⁻(CF₃SO₂)₃C⁻, CH₃COO⁻ and CF₃COO⁻ and a cation selected from thegroup consisting of alkylphosphonium, alkylammonium, N-alkylpyridiniumor N,N′-dialkylimidazolium.
 15. The process of claim 14 wherein thevapor pressure of said reactive liquid having Lewis acidity is less than10⁻⁴ Torr at 25° C.
 16. The process of claim 14 wherein the reactiveliquid for association with the gas having Lewis acidity is sufficientto provide for a working capacity within a pressure range from 20 to 760Torr of at least 0.5 mole of gas per liter of liquid and provide forevolution from the reactive liquid of at least 50% at the operativetemperature ranging from 0 to 150° C.
 17. The process of claim 16wherein the Lewis basic gas is boron trifluoride.
 18. The process ofclaim 17 wherein the ionic liquid has a cation component which isN,N′-dialkylimidazolium and the anion component is BF₄ ⁻.
 19. In aprocess for effecting storage and of a gas, in a storage and deliverysystem comprised of, i) a vessel containing a medium capable of storinga gas and ii) a regulator for delivery of said gas stored in said mediumfrom said vessel, the improvement for effecting storage by a methodselected from the group consisting of: storing a gas having Lewisbasicity in a reversibly reacted state within a reactive liquid havingLewis acidity wherein the Gibbs Free energy of reaction between the gashaving Lewis basicity within a reactive liquid having Lewis acidity isfrom about −1 to −6 kcal/mol of reactive group over a temperature rangeof from 0 to 150° C; and, storing a gas having Lewis acidity in areversibly reacted state within a reactive liquid having Lewis basicityand wherein the Gibbs Free energy of reaction between the gas havingLewis acidity within a reactive liquid having Lewis basicity is fromabout −1 to −6 kcal/mol of reactive group over a temperature range offrom 0 to 150° C.
 20. The process of claim 19 wherein the Gibbs freeenergy of reaction is from −2.5 to −3.5 kcal/mole between said gas andsaid reactive liquid at 25° C.
 21. The process of claim 20 wherein thereactive liquid is an ionic liquid and the anion component of thereactive liquid is a cuprate, aluminate, or borate and the cationcomponent is derived from N,N′-dialkylimidazolium salt.
 22. In a processfor effecting storage of a gas, in a storage and delivery systemcomprised of, i) a vessel containing a medium capable of storing a gasand ii) a regulator for delivery of said gas stored in said medium fromsaid vessel, the improvement for effecting storage by a method selectedfrom the group consisting of: storing a gas having Lewis basicity in areversibly reacted state within a reactive liquid having Lewis aciditywherein the Gibbs Free energy of reaction between the gas having Lewisbasicity within a reactive liquid having Lewis acidity is from from −2.5to −3.5 kcal/mole of reactive group at 25° C; storing a gas having Lewisacidity in a reversibly reacted state within a reactive liquid havingLewis basicity and wherein the Gibbs Free energy of reaction between thegas having Lewis acidity within a reactive liquid having Lewis basicityis from about −2.5 to −3.5 kcal/mol of reactive group at 25° C; and,wherein the reactive liquid is an ionic liquid and the anion componentof the reactive liquid is a cuprate, aluminate, or borate and the cationcomponent is derived from an N,N′-dialkylimidazolium salt.